Tapered rollers are used for a wide variety of purposes. Simply by way of example, conveyor systems for moving finished and unfinished products to various locations in facilities such as factories and distribution warehouses often use endless moving flexible belts and/or sequences of rollers, and such conveyor systems typically include tapered rollers to form turns and spiral sections of conveying paths. Another related use for tapered rollers includes web feed rollers used in the production and/or processing of paper or plastic films. Still another is for conveyor drum pulleys used at the ends of belt conveyors; conveyor drum pulleys include outer drums, side panels, and hub assemblies of various constructions that either accept shafts or have shafts welded thereto. The drum face of a pulley can be straight, or can be point crowned, trapezoidally crowned, arc crowned or machined to special shapes; in some cases grooving is included for belt tracking strips.
Tapered rollers for these and other purposes may be made from various metals, thermoplastic materials, or combinations of both. Formation of tapered rollers for apparatus of the types referenced above are often formed by a metal-spinning process, and it is to formation of tapered rollers by metal spinning that the present invention is directed. As used herein, the term "tapered rollers" refers to rollers with outer surfaces which are off-cylindrical in any of several ways, whether by constant-rate straight-profile tapering along their lengths, by multiple-taper tapering, by variable-rate tapering, by crowning, or by other kinds of variations in outer roller profiles.
Metal spinning is an old technology wherein a round metal blank is positioned over a rotating mandrel. As is known to those skilled in the art, during most metal spinning processes rotating rollers engage the metal blank while traveling inwardly along a Y-axis toward the center of the mandrel and simultaneously traveling along an X-axis. The rotation of the mandrel coupled with the X-Y movement of the spinning rollers gradually spin-forms the flat disk of material over the mandrel to produce a finished shape of which the mandrel is a mirror image.
Alternatively, in the case of the tapered rollers or pulleys, the most common industrial practice is to form such rollers by metal-forming machines known as swaging machines. Such a machine has a set of rotating rollers that directly or indirectly impact a set of dies containing a mirror image of the outer diameter of the part to be formed. By way of example, in order to form a tapered roller, a cylindrical tube or pipe is positioned on a mandrel, and the rotating rollers engage the surface of the tube to form it into the shape of the mandrel.
Similarly, pulleys are typically formed from sections of tubing or pipe. For example, when a crowned pulley is desired, the crown is formed by swaging the outside end of the tubing toward the mid-point thereof, and thereafter reversing the feed and swaging from the opposite end of tubing toward the center thereof to form a crowned center. Alternatively, a crowned pulley may be formed by using an expansion mandrel and forming the crown from the inside of the tube or by positioning an air or hydraulic bladder inside the tubing and expanding the tubing outwardly into a cavity mold that is a mirror image of the outside profile of the desired pulley.
While adequate for certain applications, prior art swaging machines have significant limitations. For example, the length and quality of tapered rollers formed by prior swaging machines has been limited by the lengths of the dies. Even in the largest swaging machines, the longest dies available are 20-24 inches in length. In order to form tapered rollers of longer lengths, multiple passes through a series of dies are required, and this adds to tooling costs, set-up times and processing times. Also, it is known that transition from one die to another often leads to visible breaks or ridges in the tapered surfaces of rollers when viewing the part as a whole. Such breaks or ridges are objectionable to some uses of such components.
Furthermore, swaging operations typically involve significant up-front capital costs. For example, differing initial diameters, finishing diameters and rates of taper may necessitate that specific dies be manufactured for each tapered roller. For larger swaging machines, such dies may cost several thousand dollars. Such high costs have acted as a deterrent to many who would seek to enter the business against competitor that already possess tooling. Moreover, swaging is a high impact, rapid hammering type of operation resulting in high maintenance costs of dies, rotating roller rings and internal parts. It can also be appreciated that use of an internal mandrel prevents the forming of drive grooves for a conveyor drum roller, and prevents the formation of tapering on opposite ends of a tube because the mandrel cannot be extracted after formation.
Swaging, air/hydraulic bladder and other mechanically-expandable mandrel methods of forming crowned pulleys do not produce concentricity or the run-out typically required by manufacturers of conveyors having high operating speeds. In addition, these methods currently only produce point-crowned pulleys having straight tapers. It is known that certain roller configurations tend to reduce the useful life spans of certain types of conveyor belts. Certain belt-friendly surface forms, such as trapezoidal crowns, trapezoidal crown, concave center and rounded crowns, are only available in pulleys having machined faces.
With these things in mind, there is a clear need in the industry for more readily produced rollers and pulleys of higher quality which can enable higher conveyor operating speeds. More generally, there is a clear need in the field of forming tapered metal rollers for an improved manufacturing equipment and methods.
The below-referenced United States patents disclose various devices that were said to be useful for the purposes for which they were intended. Without making any admissions as to pertinence to the present invention, the full disclosures of all below-referenced United States are incorporated here by reference.
U.S. Pat. No. 3,632,273 discloses a machine for converting plain plastic tubing such as polyvinyl chloride tubing and the like into simulated bamboo for use in the manufacture of furniture, etc. by forming on the plain plastic tubing a plurality of spaced peripheral ridges along the full length of the tubing. The machine supports a length of the tubing by means of pairs of rollers and heats the tubing between the rollers at the positions where ridges are to be formed as the tube is rotated. The pairs of rollers are mounted so that one roller may slide a short distance in the direction of the other roller. Upon heating, the sliding roller in each pair moves in the direction of the other roller and simultaneously forces the axial movement of the plastic tubing, forming peripheral or circumferential ridges on the plain plastic tubing. The tubing is then cooled off to cause the ridges to set.
U.S. Pat. No. 3,874,208 discloses a spinning adapter for spinning a tubular work piece to a predetermined decreased dimension. The adapter has a quill secured to the carriage of a machine tool having a headstock with a rotary chuck thereon to receive and rotate the work piece. The quill is hydraulically movable on the carriage in axial alignment with the headstock. A mandrel is adapted to be secured inside the quill at various positions and is of a size permitting insertion inside the work piece. The forward end of the quill has a plurality of circumferentially spaced reducing rollers. The rollers are journaled around the mandrel and brought into engagement with the work piece to spin the inside diameter of the work piece on the mandrel to the outside diameter of the mandrel. The reducing rollers are held in the reducing position by set screws in engagement with cam surfaces of rotatable arms to which the rollers are pivoted. The rollers and mandrel are simultaneously moved longitudinally relative to the work piece away from the headstock to accomplish the spinning operation.
U.S. Pat. No. 4,036,044 discloses a process for forming metal pipes to a desired shape and includes fitting a metal pipe onto a mold having the same profile as the one to be formed. The arrangement includes fixing the pipe thereon, and arranging a plurality of metal rollers spaced around the metal pipe. The rollers are arranged in such a manner that these rollers are in contact with the pipe and keep their centers on the circumference of a concentric circle. This is accomplished irrespective of the change in the position of the rollers during forward and backward movement of the rollers relative to the longitudinal center axis of the mold. The metal pipe is rotated with the mold in the longitudinal direction while the rollers are forced to move forwards and backwards.
U.S. Pat. No. 4,038,850 discloses a method of producing one-piece baseball bats from metal tubing by use of a forming machine without welding or joining individually processed portions. The process includes rotationally forming a portion of the body portion from the tubing which is re-chucked after working and followed by a turning over of the tubing which has been removed from the mandrel.
U.S. Pat. No. 4,047,413 discloses an automatic metal-spinning machine utilizing a plurality of work spindles which rotate about their respective axes. The machine has a parallel spinning-tool which rotates a shaft with variable pressure to apply a tool against a work piece. All the shafts simultaneously and continuously rotate around a central column so that plural metal blanks are progressively formed. Several parts are completed as the spindles and tool shafts make one revolution around the central column.
U.S. Pat. No. 4,953,376 discloses a metal spinning process and apparatus for necking-down a container. The apparatus has an open end, a closed end and generally cylindrical inner and outer surfaces. A resilient pressure bladder is inserted into the container prior to the necking-down operation. Pressure is maintained in the bladder during the operation to prevent crumpling of the container body. The invention is particularly useful for thin walled, deep drawn steel containers.